1. Field of the Invention
The present invention relates to a head for a thermally assisted magnetic recording that records data by emitting near-field (NF) light on a magnetic recording medium and by decreasing an anisotropic magnetic field of the magnetic recording medium.
2. Description of the Related Art
In the field of magnetic recording using a head and a medium, further improvements have been demanded in performance of thin film magnetic heads and magnetic recording media in view of an increase in recording density of magnetic disk devices. For the thin film magnetic heads, composite type thin film magnetic heads configured from lamination of a reading magnetoresistive (MR) element and a writing electromagnetic conversion element are being widely used.
The magnetic recording medium is a non-continuous medium, in which magnetic particles are aggregated. Each magnetic particle has a single magnetic domain. In this magnetic recording medium, a single recording bit is configured by a plurality of magnetic particles. Therefore, to increase magnetic density, the size of the magnetic particles must be reduced, and asperity at a border of adjacent recording bits needs to be minimized. However, if the size of the magnetic particles is reduced, there is a problem that thermal stability for magnetization of the magnetic particles is lowered as the volume of the magnetic particles is reduced.
To address this problem, increasing magnetic anisotropic energy Ku of magnetic particles may be considered. However, this increase in Ku causes an increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity for the thin film magnetic head is determined substantially by saturation magnetic flux density of a soft magnetic material forming a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined from the upper value of the writing magnetic field intensity, writing becomes impossible. Currently, as a method to solve such a problem of thermal stability, a so-called thermally assisted magnetic recording method has been proposed, which, using a magnetic recording medium formed by a magnetic material with large Ku, performs the writing by heating the magnetic recording medium immediately before applying the writing magnetic field to reduce the anisotropic magnetic field.
For this thermally assisted magnetic recording method, a method that uses a near-field light probe, a so-called plasmon generator, which is a piece of metal that generates near-field light from plasmon excited by emission of laser light, is known. For example, a plasmon generator that includes a metal scatter having a shape of a cone or the like formed on a substrate is disclosed in U.S. Pat. No. 6,768,556.
In addition, a configuration is disclosed in U.S. Patent Publication No. 2004/081031 A1, in which a plasmon generator is formed at a position to contact the main magnetic pole of a perpendicular magnetic recording head so that an irradiated surface of the plasmon generator is perpendicular to the magnetic recording medium.
In the magnetic recording head including such a conventional plasmon generator, the information is written such that the near-field light generated at a near-field light generating portion of the plasmon generator heats the magnetic recording medium so as to decrease the anisotropic magnetic field. However, the heat caused by the generated near-field light at the near-field light generating portion is accumulated at the near-field light generating portion. As a result, there are problems that a near-field light generating end surface having the near-field light generating portion of the plasmon generator protrudes on the side of the magnetic recording medium, and that optical-power efficiency of the plasmon generator significantly decreases. Therefore, to address these problems, it is necessary to dissipate the heat from the near-field light generating portion.
In contrast, to efficiently perform the thermally assisted magnetic recording, it is preferable to arrange the near-field light generating portion of the plasmon generator and the magnetic pole adjacent to each other. That is, it is preferable to reduce the thickness of the plasmon generator as much as possible. However, if the thickness of the plasmon generator at the near-field light generating portion is reduced, the heat escapes from the near-field light generating portion to the side of the magnetic pole. As a result, there is a problem that degradation of the magnetic pole and the like are caused.